Trans-dermal drug delivery techniques based on microneedle arrays can painlessly administer controlled amount of drugs through penetration of the epidermis.
Solid microneedles arrays can be employed in this process after coating the tip with the liquid agent before insertion. However, the volume of the liquid thereby transferred may be too small, if standard smooth-wall microneedles are employed. Use of a porous needle may be employed, but such structures are fragile and there may be implications if fragments of the needle remain under the skin after the procedure.
We have developed a low cost technique for the formation of pyramidal microneedle arrays based on crystalline silicon. A combination of crystallographic etching, thermal oxidation and subsequent HNA treatment was employed. Optimization of the process parameters led to the generation of pyramidal microneedle arrays where the tip diameter can be reduced without loss of overall structural robustness.
Employing our fabrication process, micro-cavities with size 4–10 μm in diameter can be reproducibly generated in a ring surrounding the tip, while maintaining an otherwise smooth microneedle facet wall. Optical fluorescence imaging indicates that fluids can be exclusively trapped in these microcavities. This process retains the structural stability of the overall microneedle, while enhancing the drug-transfer capabilities.
Various types of Microneedles (a) Pointed tip smooth-wall
(b) Cavity on wall
(c) Cavity surrounding tip
A cuvette is generally used in the optical testing of fluids, such as the determination of its optical absorption coefficient as a function of wavelength. The challenge in testing many organic liquids such as oils is that in the deep ultraviolet range the absorption coefficient is very high, and dilution is necessary to generate useful data.
An alternate process is to use a microCuvette with a very small optical path length so that measurements can be carried out directly on the liquid under test, thereby promoting automation.
We have developed such a system using silicon micro-fabrication technology, forming a cavity with an integrated UV-transparent optical window capable of holding 100nl of liquid, with an optical path length smaller than 300 micrometers. This is in the form of a inverted truncated pyramid with very smooth sidewalls.
Using this system, we have carried out UV absorption spectroscopy on 100 nanoliter of mixtures of commercially sourced diesel with ethanol, and diesel with kerosene.
Two zones of interest were identified in the absorption spectrum of diesel. For a 0 to 10% diesel in ethanol mixture, a clear shift of the UV absorption edge from 297nm to 336nm was observed. For the diesel in kerosene mixture a linear shift of the absorption edge from 335nm to 365nm was observed for the entire composition range.
Our results indicate that a single wavelength source and detector at 345nm is sufficient to determine the diesel in kerosene composition using this micro-cuvette, which would be very useful in detection of adulteration in fuels
Top: Scanning Electron Microscope of MicroCuvette
Bottom: MicroCuvette in the empty state, and filled with liquid.
While the use of ultraviolet radiation to de-activate pathogenic microorganisms using mercury lamps for large-volume water purification has been implemented for a long time, the more recent development of UVC light emitting diodes (LEDs) has raised the prospect of small-volume, low-power, point-of-use water purification. This has opened up the possibility of personalized container-based water purifiers employing UV-driven germicidal action, powered by rechargeable and renewable electrical energy sources.
A novel reactor was designed and implemented for water purification using deep ultraviolet light emitting diodes (LEDs). The focus was on minimizing the number of LEDs required for effective germicidal action. Simulation studies were carried out on the flow of water as well as the irradiance of UV. Variation was made in the beam divergence of the UV sources and reflectivity of optical coatings used for photon recycling.
Based on optimized reactor designs, water purification was carried out both in the static and flow-through configuration. Water from various sources was spiked with a known bacterial strain, exposure studies were carried out and germicidal effect was determined. Our results indicate that under optimal design, a 3 mL volume of water shows a three order inactivation using a single UV-LED in a static reactor in 180 s. For a flow-through geometry, only three LEDs were used in the reactor implementation, and a multi-pass procedure was used to purify 150 mL of water from an Escherichia coli CFU count of 4.3 × 104/mL to 12/mL.
While slow, this process requires less than 2 W, and can be powered from rechargeable sources. Faster processes can be implanted using multiple such reactor units in parallel, and can be optimized to the requirement and power levels.
The research on the development of Lab-on-chip systems is funded by the Government of West Bengal, and has been carried out at the RPE microLab in collaboration with the Department of Electronic Science, University of Calcutta. There are several components to the research effort.
The effort was also supported by software obtained through the NPMASS program.
Digital microfludicis systems based on the Electro-wetting on dielectrics currently under development. There is also an effort directed towards the development of micro-channels by the soft lithography technique.
Our target is to integrated optical testing systems, specifically in the UV domain, within the microfluidic system.
Both experimental and simulation studies are being carried out as part of this effort. Design of microfluidic components such as micro-channels, micro-mixers, etc is carried out using commercial software such as COMSOL Multiphysics.
